Koh Rong, Koh Rong Sanloem and southern islands
Cambodia’s best diving and snorkeling is around the islands off Sihanoukville — especially Koh Rong and Koh Rong Sanloem. Reefs are modest compared with Thailand or Indonesia, but the water can be clear, sites are uncrowded, and you may see seahorses, reef fish and the occasional larger pelagic.
The primary base for recreational diving. Several dive shops offer fun dives, Discover Scuba and Open Water courses. Snorkeling is excellent from many beaches and on boat trips.
More remote sites with potentially better coral and marine life. Usually reached on longer day trips or liveaboard-style outings from the mainland or Koh Rong.
Snorkeling rather than scuba; simple and suitable for families on a day trip from Kep.
Visibility varies (often 5–15 m). The dry season (November–April) generally brings calmer seas. Water temperatures are warm year-round; a shorty or 3 mm wetsuit is typical.
PADI and SSI centres operate on Koh Rong, Koh Rong Sanloem and in Sihanoukville. Dive centres and operators are listed at major island and mainland hubs.